Alternating-current motor.



No. 645,l30. Patented Marjia, 1900. w. e. RHODES.

ALTERNATING CURRENT MOTOR.

(Application filed Nov. 22, 1899.)

- 2 Sheets-$heat l.

' (No Model.)

No. 645,!30. Patented Mar. l3, I900.- W. G.'RHODES.

ALTERNATING CURRENT MOTOR.

- (Application filed Nov. 22, 1899.)

(No Model.) 2 Sheets-$1180! 2 Masses: 520672602;

UNITED STATES PATENT OFFICE.

i vILtIAM GOULD Rno'nns, or SALFORD, ENGLAND.

ALTERNATING=CURRENT MOTOR.

SPECIFICATION forming part Of Letters Patent No. 645,130, dated March 13, 1900.

Application filed November 22, 1899. Serial No. '73 7,888. (No modeLl To all whom it may concern:

Be it known that I, WILLIAM GOULD RHODES, asubject of the Queen of Great Britain and Ireland, residing at Salford, in the county of Lancaster, England, have invented Improvements in Alternating-Current Motors, of which the following is a specification.

This invention has reference to improvements in alternate-current motors of the induct-ion typethat is to say, those having a part to which the alternate current is supplied and another part provided with a winding or windings (hereinafter referred to as a winding) in which currents are induced. In this description it is assumed that the usual arrangement of these parts is followedviz., that the former part is stationary and the latter part rotary. These parts are respectively called the stator and the rotor. Sometimes the rotor-winding forms a closed circuit or circuits, but sometimes it is provided with contact-rings and brushes for the purpose of closing its circuit or circuits through an external circuit or circuits. hen starting such an alternate-current motor so provided with contact arrangement, it is usual to insert a simple resistance in the rotor-circuit in order to check the current in the rotor-winding to prevent excessive currents being drawn from the mains and to increase the torque on the rotor-shaft. Sometimes instead of a simple resistance a choking-coil or other arrangement giving a back electromotive force of self-induction has been employed. Nith such arrangements there is a lagging displacement of the currents in the rotor-windin g, which reduces the magnetizing action of the stator-currents and also the torque of the rotor and allows of the passage of undulyrlarge currents into the stator.

Now this invention has for its object to obtain a larger starting torque than hitherto, whether using single-phase or multiphase currents, at the same time keeping the statorcurrents relatively small. For this purpose instead of using simple resistances, as hereinbefore mentioned, or arrangements giving a back electromotive force by self-induction for checking the currents in the rotor-winding at starting, the rotor-windin g is subjected to the action of a counter electromotive force obtained directly or indirectly from other parts of the main supply-circuit and so applied as to reduce, prevent, or counteract the lag of the currents in the rotor winding or windings or even such as to cause a lead or displacement contrary to that which would be caused by self-induction.

As will be obvious, the invention can be carried out in various ways.

Figures 1, 2, 3, 4, and 5 are diagrams simply showing, by way of example, different ways in which the invention can be carried into practice.

In the arrangement shown in Fig. 1, a is the stator-winding, b the rotor, and c c the alternate-current-supply mains. The rotor-winding is connected by means of the ordinary contact-rings e, brushes f, and conductors g to a switch, whereby it can be connected to suitable portions of the stator-winding in such a way that the opposing electromotive force that can be thus applied to the rotor-winding at starting can be gradually diminished as the speed of the rotor increases and, if required, finally cut out altogether when full speed is attained. In the example shown the switch comprises a movable contact or slider 71, that is electrically connected to one of the conductors g, and a series of insulated fixed contacts 7t, that are electrically connected to different points Z of the stator-winding a and one of which is also connected to the other conductor g. With this arrangement it will be seen that when the contact 2 is moved into the position shown in full lines the maximum counter electromotive force the arrangement is capable of producing can be impressed upon the rotor-winding at starting and that by moving the contacti in the direction of the arrow the counter electromotive force impressed on the rotor-winding can be gradually reduced, and when the said contact assumes the position shown in dotted lines will be finally re moved altogether.

\Vhen a starting-resistance is used in connection with the stator-winding, the required counter electromotive force may be obtained therefrom by using the difference of potential across portions of the said resistance, as shown, for example, in Fig. 2, where the fixed contacts of the switch are connected to different points a of the stator starting-resistance 0.

'When the pressure of the electric supply used for driving the motor is not suitable for providing the required counter electromotive force for starting, a transformer maybe used to provide the necessary counter electromotive force. The transformer may be of the so-callec autotransformei type or one of the ordinary kind and the required variable counter electromotive force be obtained by tapping suitable portions thereof or by varying its pressure in any known or suitable way-as, for example, by inserting a resistance in either its primary circuit or its secondary circuit. Fig. 3 shows one arrangement of this kind wherein the switch to which the conductors g are connected has its fixed contacts 7c connected to different points 19 of the winding (1 of an autotransformer, which is connected up to any suitable part of the motor or supply circuit or circuits, so that by movingthe contact t' the counter electromotive force impressed on the rotor-winding can be varied.

Fig. 4 shows a modified arrangement wherein the fixed switch-contacts are connected to different points of the secondary winding 1" of an ordinary transformer, the primary winding 3 of which is connected up to some suitable part of the motor or supply circuit or circuits. The switch is connected up to the rotor-winding, as in the other examples, so that a back electromotive force of variable amount can be impressed upon the rotor-windin g as required.

Fig. 5 shows a further arrangement in which the conductors g are connected to the secondary winding 0* of an ordinary transformer, and the electromotive force thus obtained is duced either by gradually inserting a resistance If in the primary winding 5 or a resistance t in the secondary winding 9", so as to gradually reduce the counter electromotive force impressed on the rotor-winding at starting.

In the diagrams for simplicity only one pair of brushes is shown. It is to be understood,

however, that each arrangement is intended to be applicable to any kind of induction-motor, either single phase or multiphase, and with the rotor-winding in two or more circuits.

The switch used in carrying out the invention may be of any suitable form; but one is preferred in which the slider is provided with a resistance to avoid short-circuiting adjacent fixed contact-pieces as it passes from one fixed I contact-piece to another. This construction of switch is well known.

With each of the arrangements described or other arrangements embodying the same principle there is impressed upon the rotorwinding a counter electromotive force such that the tendency of the current in the rotorwinding to lag is prevented or reduced or counteract-ed, and in consequence the magnetizing action of the stator-currents and the torque of the rotor are increased.

WVhat I claim is- 1. The combination with an alternate-cur rent motor of the induction type, of means whereby there can be impressed upon the rotor-winding at starting, a counter electromotive force'derived directly or indirectly from the main supply-circuit and which will re duce, prevent or counteract lagging displacement of phase of the currents induced in the rotor-winding by the stator.

2. In an alternate-current motor of the induction type, the combination with the stator and rotor windings of variable contact devices whereby the said rotor-winding can be connected with different points of the stator-Winch ing between which points there is a difference of potential.

3. In an alternate-current motor of the induction type, the combination vith the motor-circuit and rotor-winding, of a switch and electrical connections wherebyportions of the motor-circuit can be successively tapped so as to impress a gradually-decreasing counter electromotive force on the rotor-windi ng when starting the motor.

Signed at Manchester, in the county of Lancaster, England this 6th day of November,

WILLIAM GOULD RHODES. WVitnesses: A

J AMES M. HEWITT, ELDON A. KING. 

